This invention is directed to a window assembly incorporating a seal and more specifically a composite seal and to a method for forming such an assembly.
A window, such as an aircraft type of window is mounted on a frame 8 which is part of the structure of the vehicle. As shown in FIG. 1, an exemplary aircraft window (i.e., window transparency) 10 is a laminate structure and includes one or more main plies 12 which are typically made out of a polycarbonate, acrylic or glass. An interlayer 14 typically made of polyurethane or polyvinyl is bonded on an outer face of the main ply. A face ply 16 is bonded on top of the interlayer. The face ply is typically made of glass but may also be made of plastic. A heater layer or coating 15 may be applied to the inner surface of the face ply allowing for the heating of the face ply for purposes of defrosting, and the prevention of ice build up on, the face ply.
The face ply does not extend to the ends of the main ply. As such, an end portion 18 of the main ply is not covered by the face ply and interlayer. This end portion is mated to the frame 8. Typically, the end portion of the main ply is fastened to the window frame using fasteners 20, or may simply clamp an end portion of a windshield.
When the main ply is mounted to the frame, a gap 22 is left between an end of the frame and the ends of the face ply and interlayer. This gap allows for expansion and contraction of the window, i.e., the main ply, the face ply and interlayer. The gap is sealed with a sealant, typically a polysulfide sealant, which fills in the gap and extends over the face ply forming a hump seal 24 for preventing moisture from entering through the gap. Such moisture can cause delamination the window 10. Typically, the hump seal extends a distance 26 about half an inch over the face ply.
By extending over the outer surface of the face ply, the hump seal is exposed to the outer environment, and is consequently susceptible to erosion, cracking and lifting which results in the intrusion of moisture into the laminate structure of the window 10. As a result, hump seals have to be frequently inspected and repaired to prevent window delamination and/or heater layer failure.
Another problem with hump seals is that they are costly to manufacture in that they require a specific amount of sealant of a specific thickness to extend a specific amount over the face ply. As a result, the process of forming and controlling the hump seal is very labor intensive. The hump seal can also fail due to the delamination of the edge of the face ply abutting the hump seal. Additionally, major expenditure and effort is required to disassemble the window assembly for purposes of seal repair due to the bonding of the seal to the frame and plies.
A further problem with conventional aircraft window assemblies is that with time the face ply separates, i.e., delaminates, from at its edge from the interlayer 14, and/or the interlayer 14 and face ply delaminate from the main ply. This delamination also results in failure of the seal and is a frequent cause of aircraft window failures.
As such, a seal between the frame and face ply and/or window assembly incorporating such a system is desired that is more resistant to erosion, cracking and lifting and provides more resistance to face ply edge delamination and which is easier to manufacture and overhaul.